Process of combined absorption and fractionation for recovering gaso



Dec. l1, 1928. 1,695,139

` E. R. COX ET AL PRocEss 0F COMBINED ABsoRPTIoN AND FnAc'rIoNA'rIoN FonREcovERINe GAsoLINE FRou sans Filed Aug. 3l, 1926 @Jbsa .lion Ton/ r'-Patented Dec. l1, 1928.

UNITED STATES PATENT OFFICE.

EDWIN R. COX AND DEXTER A. GUSIIMAN, OF LOS ANGELES, CALIFORNIA.

PROCESS F COMBINED ABSORPTION AND FRACTIONATION FOR RECOVERING GASO-LINE FROM GAS.

Application filed August 31, 1926. Serial No. 132,720.

Our invention is a process and apparatus oit combined absorption andfractionation for recovering gasoline from gas, being particularlyadapted ior recovering gasoline from natural gas.

An objectof our invention is a combination of an absorption andfractionating process in which the suitable condensable vapors innatural gas are absorbed in an absorbing column and at the same timethis column Mfunctions to condense, evaporate and recondense the suit-Vable vapors by a fractionation process.

In recovering gasoline from natural gas by an absorption process, it isusual to absorb as much as possible in an absorption column or tower ora series of saine, or in horizontal type absorbers. The absorption oilis then. distilled, the gasoline being separated and condensed. In thevarious steps of separating the useless or injurious gases and oilstroni the gasoline, this is done by weathering or some process ofrectiiication. In weathering the product, heavy losses are entailed,while the usual rectifying processes are quite expensive, involving theuse ot costly compressors and other equipment, as Well as theconsumption of considerable power.

An object oi our invention is to selectively7 absorb the valuablecomponents 'from the natural gas in an absorbing oil with as little aspossible of the injurious fractions. These are assumed to be mainlymethane, eti-haue and propane. This will be accomplished by combiningthe ifractionating features with the absorption process. f

As is known in the absorption process, the absorbent oil becomesheated-by the latent heat of evaporation of the gasoline `absorbed andby the heat of compression oit the fixed gas absorbed, thus giving adifferent temperature between the ends of the absorption column. In ourinvention we maintain this difference of temperature in the absorptiontower' greater than that normally due to the latent heat oic evaporationof the gasoline absorbed and the heat of compression ot the fixed gasabsorbed.

In an absorption process using an absorption tower, the absorbent oilflows downwardly and the Wet gas upwardly into intimate Contact with theoil. In fractionating or recti'iying the process is very similai, thedownilowing liquid being reliuX obtained by pai'- tially condensing theupwardly flowing vapors, these being the vapors in counter-flow to thecondensate. A condition that is essential ibr ifracti-onating is aproper temperature gradient between the top and bottoin olf the tower.The top must be cold enough to condense all the vapors it is desired toretain and the bottom hot enough to evaporate all it is desired toexpel. In an absorption process we iind that the absorbent oil is heatedbetween l() to 200 F. or an average otl 1Y0 F. due to the latent heat otevaporation of the gasoline condensed and the` heat of coinpression ofthe fixed gases absorbed.

A. characteristic oi' our invention is in an absorption tower torefrigerate part of the absorbent oil and flow same into the upper partof an absorption tower and at a lower level `flow a body of absorptionoil cooled to a temperature readily obtained by ordinary water coolingto atmospheric temperatures. The oil at the base 0l the tower ismaintained at a relatively high teii'iperature either by the heat ofcompression of the wet gas forcer into thetowcr, or by suitable heatingcoils.

IVe ail ange our apparatus to include a coolingdeviee, preferably watercooled, for the absorient oil, and by means oit' suitable valves pas-isome oi the cooled oil through a refrigerator and discharge saine at thetop oi an absorption tower. Another part of the water cooled oil passedinto tbe absorption tower below the top. The oil pipes are provided withsuitaiiile valves sothat if desired the oil may be by-passed around therefrigerator and all discharged at the top of the tower withoutrefrigeration, or shut ofi the supply of oil to the mid position of thetower and pass all 0i same through the refrigerator. The wet gas is fedto the lower end of the tower under compression and preferably maintainsits heat of compression without being cooled, and also in the base otthe tower we provide heating coils in the accumulated absorption oil,for raising the oil at the base of the tower to the desired temperatureto get the desired temperature gradient between the top and bottom ofthe tower.

`Our invention will be more readily underl pipe F.

stood from the following description in connection With the drawings,which illustration is a diagrammatic View of a plant for the coinbinedprocess of absorption and fractionation for recovering gasoline fromnatural gas.

fi. cooler is designated by the numeral 1 and preferably of the Watercooled type, being indicated by a tank 2 with an irlet Water pipe 23controlled by a valve 1land an outlet Water Such Water preferably iscooled in atmospheric cooling; towers or the like.

rlhe absorbent oil is fed through a pipe 6 having Va valve 7, the oilpassiiig` through coils 8 in the Water and being` conducted out throughthe pipe 9. A refrigerator 10 is of any suitable character, haring flouTpipes 11 for the refrigerant. A valve 12 controls the flow of absorbentoil through the pipe 18 into the refrigerator and hence through the pipe14 vto the upper part 15 of the absorption tower 1G. 'l he ren'iainderof the oil continues through the pipe 17, passing through 'the valve 1Sinto what may be termed mid position 19 inthe absorption tower.

A luy-pass pipe 2O is provided having a Valve 21 so that by shutting offthevalvc 12 some ofthe oil may be by-passed around the refrigerator fromthe pipe 9 to the pipe 14.-, or if the valve 18 is also closed all theoil may be by-passed from the refrigerator. valves 18 and 21 are closedall 'the oil Will be passed through the refrigerator.

The Wet gas enters through a pipe 22 after being compressed as indicateddiagrammatically by a compressor 23 and Without any subsequent coolingAafter beingl compressed. The dry gas discharges through the pipe 24;,

` this preferably being controlled by a valve 25. The absorbent oilaccumulates in the bottoni 26 of the tanlr and heating,` coils 27 arevimbedded in this body'of oil, such pipes -becontrolled by valves 28.The absorbent oil with the gasoline content is discharged through thepipe 29, beine' controlled by a valve .30.

In. the cooler 2, While illustrated as of the Water cooled type, inpractice ive cool the Water by atn'iosphcric Water coolers that theWater is at substantially the temperature of the air. Therefore, theabsorbent oil passed through the coils in becoming cooled to about thetei'i'iperature of the Water acquires what might be termed an airtemperature, so that in effect the absorbent oil is air cooled.Therefore the oil discharging in the midposition 19, While cooled byWater, is of substantially the air temperature.

r"he operation of our method and plant is substantially as follows:-

le cool the absorbent oil to as low a teniperature as practical, byWater, to at1noslf the Lee-5,139

by proper control of the valves 12 and 18, the valve 21 being` presumedclosed so that about 60 to 80% is introduced at an intermediate level,ythis being preferably about two thirds the ieigght of the tower asindicated by thel discharge 19 of the Water cooled oil. The remainder ofthe absorb-cnt oil passed through the refrigerator 10, this being`substantially 20 to 10%, is cooled to a temperature of 30 to 40C F. andintroduced at thetop of the tower as indicated by the numeral 15. T heoil at the bottomA of the tower is heated to a suitable temperature byeither relying on heat of compression of the wet gas introduced or byusingI heating` coi ls.

The wot gas previously coiiuaressed, as in u ponia] process, is notcooled but introduced with a portion or all lof its heatof compres sion,thus beingl at a temperature of substantielly 2500 F. On account of theweight of the being.; b much less than that of the oil, the oil is notheated vto this full temperature but to a ten'iperature of approximately6() to 11)O ll". Should the temperaturek of the oil not be that desired,it may be additionally heated by the heating coils 27, or these coilsmay be relied upon substantially entirely to give the proper temperaturedifference.

By the above procediiire we maintain substantially a temperaturegradient of approximately 60D F. between the top and the bottoni of Atheabsorption tower, instead of the usual temperature gradient of about 150F., this decided temperature lrgradient being a characteristic featureof our invention.

It is obvious that our invention asdescribed above may be d giarted fromin dif feront features. For instance, all the oil .may be introduced atthe top of the absorber at atmospheric temperatures such as 60 to 70DF., being' Water cooled, this beine done by bypassing the oil around therefrigerator as above described. As an alterna-tive procedure, all theoil may be refrigerated to a suitable temperature Vand introduced at thetop of the tower, this bei done by closing' both the valves 18 and 21.As above, mentioned the temperature of the bottoni oil in the'absorbermay be maintained at the proper degree by the heat of comin-essieu ofthe Wet gris passing into the tower, by a heating; coil in the oil or byboth, or if desired steam may be injected into the bottom of the towerfor heating. l

From the above description it Will be seen vthat We have provided anabsorption plant in which the temperature gradientin the absorptioncolumn is much greater than that usually used so that the temlieratureof the oil may be increased by the latent heat of evaporation ofthegasoline absorbed and the heat of the compressed or fixed gas absorbedandstill leave a decided difference of temev perature between the oil atthe top and the bottom ofthe tower. This large difference loi oftemperature causes a fractionating or rectifying operation on the wetgas by causing a continuous condensation and evaporation of theConstituents of the gas, thereby enabling us to obtain an absorbedproduct which embodies the principle of desirable condensable oils andhas passed with the dry gas the undesirable non-condensable gases.

' The elimination of these undesirable constituents which are mainlymethane, ethane and propane in the usual process, is complicated andcostly. We estimate that they take up approximately one half theabsorptive capacity of the absorbing menstruum. By eliminating them asabove described, we are able to reduce the size of the other pla-ntequipment, such as stills, evaporators, dephlegmators, exchangers,preheaters, coolers, condensers, recompressors, rectifier-s, etc., andso substantially lower the cost of the plant.

It is obvious that our invention may be applied to different types ofabsorption plants or apparatus, and that the general features andspecific details of our invention both as to the method and apparatusmay be considerably changed wit-hout departing from the spirit thereofas set forth in the description, drawings and claims.

Having described our invention, what we claim is:

l. The process of combined absorption and fractionation for recoveringgasoline from natural gas, comprising cooling an absorbent oil tosubstantially air temperature, refrigerating part of this oil to aconsiderably lower temperature, flowing the refrigerated oil downwardlythrough an absorption tower, flowing the air temperature oil downwardlythrough a lesser portion of the absorption tower and flowing compressedwet gas without precooling, upwardly through the absorption tower.

2. The process of combined absorption and fractionation for recoveringgasoline -from natural gas, comprising cooling an absorbent oil tosubstantially air temperature, refrigerating part of this oil toslightly above freezing temperature, passing the refrigerated oildownwardly through an absorption column, passing the air temperature oildownwardly through a lesser portion of the same absorption column,passing wet compressed gas without precooling upwardly through thecolumn, and drawing off dry gas at the top of the column.

3. The process of combined absorption and fractionation as claimed inclaim 2, in addition applying heat other than that of the heat ofcompression of the wet gas to the absorbent oil in the base of theabsorption column. i

4. A process of combined absorption and fractionation for recoveringgasoline from natural gas, comprising cooling an absorbent oil tosubstantially air temperature, refrigerating about one third of the oilto a temperature slightly above freezing, passing said oil downwardlythrough an absorption column, passing the balance of the oil downwardlythrough the same absorption column, through a lesser distance from thebottom, passing wet compressed gas without precooling upwardly throughthe absorption column, drawing off the dry gas at the top and heatingthe absorbent oil in the base ofthe tower to approximately 100O F.

5. A process of combined absorption and fractionation for recoveringgasoline from natural gas, comprising cooling an absorbent oil tosubstantially air temperature of to 700 F., refrigerating substantially20 to 40% of such oil to about 30 to 40 F., passing such refrigeratedoil downwardly through an absorption column, passing the remainder ofthe absorbent oil downwardly through the same column through a lesserdistance, passing compressed wet gas without precooling upwardly throughthe column, and maintaining the temperature of the absorbent oil in thebase of the column at. substantially to 110 F.

6. The process of combined absorption and fractionation to recovergasoline from natural gas, comprising introducing absorbent oil into anabsorption column at the top and at a position substantially one thirddown from the top, cooling the whole of the oil to substantially airtemperature prior to introduction, utilizing part of the oil afterrefrigeration for introduction at the top of the column, by-passing someof the air temperature oil into the top to secure the desiredtemperature gradient of the column, and introducing wet compressed gasinto the base of the column.

7. The process of combined absorption and fractionation as claimed inclaim 6, maintaining the temperature of the absorbent oil at the base ofthe column at a higher temperature than that produced by heat ofcompression of the wet gas.

8. An apparatus for the combined absorption and fractionation for therecovery of gasoline from natural gas, comprising in combination anabsorption tower having a first inlet for oil at the top, a second oilinlet positioned below the top, an inlet for wet gas at the bottoni, anoutlet for dry gas at the top, means to cool a body of absorption oil tosubstantially air temperature, means to refrigerate part of said oil,means to pass said refrigerated oil into the first inlet, and means topass some of the air cooled oil into the second inlet.

9. An apparatus for the combined absorption and fractionation as claimedin claim 8, having means to by-pass the air cooled oil around therefrigerating means.

l0. An apparatus for the combined ablll) inlet, o refrigerator, andpipin Sorpt-ion and fractionation for recovering gasoline from naturalgas, comprising ill COIB- bination on absorption tower, o rst oil inletat the top, n second oil inletpositonod belOW the top, a oompreSSOl forWet gas, means to conduct said gosk Without substantial cool ing to thebasev ofthe tower, an outlet at the top for dry gas, a coolerforvabsorption oil7 u pipo leading from same to the second oil l t0Conduct part of the cooled oil through tie refrgera tor to the first topinlet.

- 11i An apparatus for the combined absorption and fractionation forrecovering gasoline from natural gas as claimed in claim l0, having apipe to byrpass some of the cooled oil around the refrigerator andvalves to oontrol the flow of oil through the refrigerator to the secondoil .inlet and through the bypaSS. Y

In testimony whereof We have names to this spec-ilication.

EDWIN R, COX. DEXTER A. CUSHMAN.

signed our

